Volume control device



Sept. 12,1933. E. G. LODGE VOLUME CONTROL DEVICE Filed May 10, 1930 2Sheets-Sheet l Sept. 12, 1933. LODGE 1,926,206

VOLUME CONTROL DEVICE Filed May 10. 1950 2 Sheets-Sheet 2 29 Will/ 3gym, I ry/IA:

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Edmund G- Lodge Patented Sept. 12, 1933 UNITED STATES PATENT OFFICE toHugh H. Eby, Fhiladelphia,

Application May 10, 19%. Serial No. 451,326

9 Claims.

My invention relates to variable resistors, particularly the type usedfor controlling volume of reproduction in radio receiving circuits.

One of the objects of my invention is to provide a variable resistor orpotentiometer which when used for control of volume in a radio circuitgives quietness of operation and which has a long life of usefuloperation.

Another object of the invention is to provide a simplified ruggedstructure which is easily and cheaply made, being particularly adaptedto quantity production, and requiring practically no subsequent repair.

Other objects of the invention will appear as the descriptionprogresses. In the drawings:

Fig. 1 shows a side elevation view of a completely assembled variableresistor embodying several features of the invention.

Fig. 2 is a bottom view of the resistor, the bottom cover plate of Fig.1 being removed.

Fig. 3 is a fragmentary view corresponding to Fig. 2 except that itillustrates an unfinished operation.

Fig. 4 is a section, reduced in size, of Fig. 1

taken on line 4-4.

Fig. 5 is a fragmentary section of Fig. 1 taken on line 5-5. I

Fig. 6 is a perspective view of my novel contact arm for the resistor.

Fig. 6--a is a side view of a modified form or" contact arm.

Fig. 7 is a perspective view of the supporting structure for the arm ofFig. 6.

Fig. 8 shows a sectional view of the end of the resistor shaft of Fig. 1with the support of Fig. 7

secured thereto.

Fig. 9 is a view similar to Fig. 1 showing structure for combining tworesistors for simultaneous operation.

Fig. 10 is a reduced sectional view of Fig. 9 taken on the line 10-10,omitting the partition.

Fig. 11 shows a fragmentary sketch of means for coupling the shafts ofFig. 9.

Fig. 12 is a sectional view of the same means, taken on lines 12-12.

Fig. 13 is a bottom view of portions cut away to show one means forobtaining a taper.

Fig. 14 is a sectional view of the resistor element and the taper means,taken on line 14-14 of Fig. 13. I

Like reference thruout.

Referring to the drawings in detail: 1 represents the contact arm havingstruck out hook figures denote the same parts tor.

the resistor with portion 2, and bent back portions 3. Conjugate armmember 4 which is secured to the end of shaft 5 by screw 6, acts as afulcrum for arm 1, slots or sockets '7 being provided to receive fingerportions 3. There is likewise a hook portion 8 struck out from 4, and acoil spring 9 resiliently connects 2 and 8 causing 3 to bear firmlyagainst '7. Contact tip 10 is caused to bear uniformly against the edgeof the wire-wound resistor element 1]..

Casing with insulation strip 13 and said casing. 14 is a disc ofinsulation fastened as by rivets to housing 12, and supporting thebushing in which the shaft 5 turns. A spring washer W is insertedbetween shoulder 5 of shaft 5 and the bushing or bearing 15 to give firmcontact. The extensive area of 14 between the housing 12 and. shaft andbushing or grounded metal panel 16 of the radio set reduces to a mini- 7mum the capacitance associated with the resis- It is desired that suchcapacitance be reduced to a small value when the resistor is useddirectly in a radio frequency path for reasons well known in the art. 17represents insulating washers to insulate the shaft from the metal panel16, suitable locking nuts 18 being used.

The housing is sealed by means of metallic disc 19 which is secured inplace against shoul der 30 by split ring 20 which fits in groove 30.This provides a casing which is practically air tight, and easilyaccessible. In some instances I have omitted the ring 20 and formedtheedge 30 over against 19 applying lacquer to the casing to make apermanent seal.

For best operation I have discovered that the presence of pure mineraloil on the wire and contact surface materially reduces corrosion, givesbetter electrical contact, smoother mechan= 9 ical action, and makes forstill quieter operation in varying of volume of reproduction. Thishousing is especially adapted to retain a small amount of oil in thebottom, and the oil is picked up by the end of the rotating arm 1 anddistrib= uted around the resistor element.

Abutment pin 21, Figs. 1 and 5, cooperates with pin 22 to limit rotationof the shaft and contact arm 1. Pin 21 extends thru the flange of thebushing 15 into a keyway in disc 14 as shown for purposes of assembly.

Another novel detail in my construction consists in the means for firmlyand simply holding the arcuate resistor element 11 in engagement withthe walls of the casing. This means consists in a toggle element 23specifically in the form 12 is a one-piece metallic stamping, interposedbetween 11 of a bowed clamp and screw 24, better shown in Figs. 2 and 3.In place of the screw a rivet may be used or it is possible to simplybend 28 downward relying merely on the set of the metal to hold it. Theupturned ends 23 form an acute angle with the core of the resistorelement.

As shown in Fig. 3 the resistor element is inserted in the positionshown, the lower edge resting on the insulation disc i i. Next the screw24 is turned, spreading the ends of 23 outward and exerting considerablepressure upon the ends of resistor element 11, forcing said elementoutward against the walls of casing 12 thruout its length. This firm fitprevents displacement of the risistor element, assists in maintainingthe turns of wire in place due to the clamping action between the coreof 11 and the liningstrip l3, and further aliows good heat conductionfrom the element 11 to the metal casing 12.

Electrical connection is made between the ends or the resistor elementand the terminal members and 25 which are carried disc it, by means ofleads which may be continuations of the wire on the resistor element; insuch case at least one of these leads copper plated to reduce theresistance so that a close approximation,

to zero is obtainable when the contact arm is in zero position. For thesake of ruggedness and lowerin of resistance, I prefer to use relativelyheavy copper conductors for these leads, solderthe ends of the resistorelement. I have found that there are no ordinary methods of soldering tofnichrome (nickel-chromium) wire so I prefer to copper plate the endturns of the resistor element, as in application M38496 to Lodge and DaCosta filed March 24, 1930, and thensolder to the copper plating at 27.I also prefer to obtain a taper on one end of the element by a. lowresistance metallic plating, this being disclosed and claimed in thissame copending application. This taper is shown in Figs. 13 and 14,section 28 representing the plated wire.

The construction of my device is such that two of them can readily becombined to operate simultaneously as shown in Fig. 9. Substantially nospecial apparatus is necessary except a curved band 29 which holds thebases of the housings together at 30, and the insulated coupling element31 shown in Figs. 9 and 10, and in more detail in Figs. 11 and 12. Ihave found that in dual volume controls, depending upon their relativepositions in a radio circuit, a slight electrical disturbance in one ispicked upby the other and amplifled in the circuit. To minimize thisdisturbance I propose to insert one of the plates 19, to act as ashield, in one of the housings, cutting a hole 19 for the couplingelement 31. Plate 19 is in electrical contact with the housing. In thiscombination construction it is frequently advisable to ground themetallic housing, and sometimes it is advisable to do so in the singleresistor.

I have found that my improved construction gives a practically noiselesscontrol action. The hinged contact arm actuated by the coil springcauses the arm to bear on the wire with considerable pressure which isuniform. I have found. this much superior to the usual constructionwhich depends upon the resiliency of the arm itself to provide thecontact pressure. This old type is very critical in adjustment, an axialdisplacement in the shaft or variation in the level of the resistorelement resulting in a large variation in pressure. Furthermore, I havefound that for a given contact pressure the action of my improved arm issmoother. Altho very fine wire, e. g. size #38 to #48, is'- used thereis no rupture or displacement of the wires, even with the relativelyheavy contact pressure used and operating life tests have shown anequivalent life of several years with imperceptible wear.

While Fig. 1 shows an actual hinge construction it is possible to obtainsubstantially the same eiiect by equivalent constructions, for exampleas shown in Fig. ii-a. Here a portion N of the arm is necked in so thatthe arm is substantially free to flex at this portion. The spring 9provides most of the contact pressure. It is also possible formanufacturing purposes to make the entire arm of material as thin asportion N, resorting to well known methods of longitudinal ribs or bentedges to strengthen. portions 4 and 1 While I have illustrated myinvention in connection with wire-wound resistors it is obvious the samefeatures of my invention may apply to other types, e. g. the highresistance impregnated paper hind. In Fig. 9, altho both resistors areshown. as the wire -wound type, one may be of a different kind.

There may be other modifications made by those skilled in the artwithout departing from the principle of my invention. I, therefore, donot desire to limit myself to the details shown and described.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

1. A housing for a volume control resistor comprising a stamped sheetmetal cylindrical wall with an integral inwardly disposed flange portionat one end thereof, an insulation disc extending from wall to wall andsecured to said flange portion inside the bend of the flange, a shaftand contact arm rotatably supported in said disc, a resistor stripdisposed circumferentially about the inner face of said wall, supportedfrom said wall and insulated therefrom, the lower edge of said stripresting on said disc and terminals on said disc for said resistor.

2. A housing for a volume control resistor comprising a stamped sheetmetal cylindrical wall with an integral inwardly disposed flange portionat one end thereof, an insulation disc extending from wall to wall andsecured to said flange portion inside the bend of the flange, a resistorelement within said housing resting directly on said disc and a shaftbearing a. contact arm for said resistor rotatably supported in saiddisc.

3. A variable resistor comprising a. housing having a cylindrical metalwall, a flange portion on one end of said wall, a circular disc ofinsulation within said housing secured to said flange and forming withsaid flange an end closure, a shaft rotatably supported in said disc,:1. shoulder at the other end of said housing and a. metallic discsupported by said shoulder and closing the other end of said housing,making a tight joint with said housing.

4. A variable resistor comprising a housing with a cylindrical wall, acircular resistor strip disposed circumferentially on the inner face ofsaid wall and having a space between adjacent ends of said strip, aradially workable member intermediate and engaging said ends, adapted tospread with radial movement and means for partially and progressivelystraightening the member intermediate the said ends and spread thestrip.

thereby 5. A variable resistor comprising a housing with a cylindricalwall, a circular resistor strip disposed circumferentially around theinner face of said wall with the ends of said strip adjacent each.other, a bowed clamp inside the wall with the concave side thereoffacing radially outward and means for compressing said clamp toward saidwall to exert pressure endwise on said strip.

6. A contact arm for a variable resistor having a rotating shaft,comprising a pressed metal plate having angularly adjustable screwconnection with the shaft on the end of the shaft at the axis thereof,an ear on the plate near the shaft extending some distance back alongthe shaft, a contact arm portion hinged to the plate for contactingtoward its outer end with the resistor, a second ear intermediate theresistor and first ear and a tension spring connecting the ears.

7. A contact arm for a variable resistor comprising a fulcrum plate withslots, said plate having screw connection with the shaft on the end ofthe shaft at an extension near the shaft for some distance back alongthe shaft, a contact arm member the axis thereof and having in hingedrelation with said plate, having members engaging said slots and havinga second extension generally parallel to the first and intermediate theresistor and first extension and a tension spring stretched between theextensions.

8. A contact arm for a variable resistor comprising a fulcrum plate, acontact arm member having bent Z-shaped fingers on the top thereof forengaging said fulcrum plate, a tension spring anchored to the bottom ofsaid plate and said arm member respectively, whereby the latter ismaintained in engagement with said fulcrum plate and biased to rotatetoward said spring.

9. A contact arm for a variable resistor comprising a fulcrum plate,slots in said plate, a hook member struck out from said plate below thesurface thereof, a contact arm member with fingers at one end bent upabove the surface thereof and in hinged engagement :with said slots, asecond hook member struck out from below said arm member and a coiltension spring suspended between said hook members.

EDMUND G. LODGE.

